A transpiration fuel which has occurred within a fuel tank poses a cause of air pollution. A vehicle loaded with an engine, therefore, generally has a transpiration fuel treatment apparatus installed therein for suppressing the discharge of the transpiration fuel into the atmosphere. The transpiration fuel treatment apparatus, for example, connects the fuel tank and an intake system of the engine by a purge pipe line equipped with a canister. In this configuration, the transpiration fuel generated within the fuel tank is once adsorbed to activated carbon within the canister and, in accordance with a manifold vacuum in the engine, the fuel adsorbed to the activated carbon is introduced into the intake system of the engine and burned together with fresh air.
In recent years, vehicles provided with drive motors along with engines, such as plug-in hybrid vehicles (PHEV) and hybrid electric vehicles (HEV), have been put to practical use. With such a vehicle with the drive motor, a period during which the engine is stopping, namely, the period during which no fuel can be introduced from the canister into the intake system of the engine, may last for a relatively long time. Thus, a so-called sealing transpiration fuel treatment apparatus, in which a sealing valve is provided between the fuel tank and the canister, and this sealing valve is in a closed state during the period of an engine halt, is under development.
With such a transpiration fuel treatment apparatus, when the fuel tank is sealed with the sealing valve, there may be a situation, for example, in which fuel within the fuel tank evaporates due to a rise in the ambient temperature or the like to raise the pressure inside the fuel tank. If the internal pressure of the fuel tank is elevated during refueling, a transpiration fuel is likely to be discharged to the outside when a fuel filler port is opened. To deal with this situation, a transpiration fuel treatment apparatus is available in which at the time of refueling, opening of the fuel filler port is temporarily prohibited and, during this period, the sealing valve (blocking valve) is opened to lower the internal pressure of the fuel tank to a predetermined pressure (see, for example, Patent Document 1).